The present invention relates to the field of communications and more particularly to radiotelephone communications methods and systems.
Conventional cellular communications systems (such as systems operating according to the IS-136 standard) generally provide one-to-one communications from one mobile terminal to another mobile terminal or to a landline telephone coupled to a public switched telephone network. A conventional cellular communications system is illustrated in FIG. 1. This system includes a mobile switching center (MSC) 31 and a home location register 33.
The MSC is coupled to a plurality of radio base stations (RBS) 32 wherein each RBS 32 defines a cell 35. In addition, the MSC can be coupled to a public switched telephone network (PSTN) 36. As will be understood by those having skill in the art, the conventional cellular communications system of FIG. 1 can provide cellular radiotelephone communications for one or more cellular mobile terminals (MT) 37. More particularly, the cellular radiotelephone communications can be provided using conventional cellular standards wherein a telephone is dialed to place a call to another communications device.
Each radio base station provides radio frequency transmit and receive functions and supports low level protocol functions. Moreover, a radio base station can be considered a dumb peripheral of the MSC 31 wherein the MSC provides central intelligence for the system. Each radio base station can be coupled to the MSC 31 via communications links 39. These communications links can be T1 links provided, for example, via landline or microwave. The MSC 31 provides voice path switching between two cells or a cell and the PSTN 36. The MSC 31 provides central system intelligence to control the radio base stations and to process high level protocol messages from mobile terminals 37 relayed by the radio base stations. In other words, the MSC handles call setup, paging, handoff, and call connection.
The home location register 33 keeps track of the current status of the mobile terminals. For each mobile terminal, for example, the home location register can record whether that terminal is on, off, or busy, as well as the location area (including a group of cells) within which the mobile terminal is located. The home location register can also include a database of restrictions and allowed service features for each mobile terminal. The home location register can also be considered a portion of the MSC.
The setup of a call between mobile terminals 37 using the system of FIG. 1 is illustrated in FIG. 2. As shown, the originating mobile terminal 37a issues an origination message which is received by the radio base station 32a for the cell 35a in which the mobile terminal 37a is located. According to the IS-136 standard, a conventional origination message may be sent over time slots in a plurality of time division multiple access (TDMA) time frames. The radio base station 32a checks the origination message for errors, and if no significant errors are detected, the radio base station 32a forwards the message to the mobile switching center. The mobile switching center authenticates the originating mobile terminal 37a and analyses the called number. If the originating mobile terminal and the called number are valid, the mobile switching center instructs the radio base station 32a to assign a Digital Traffic Channel (DTC) to the originating mobile terminal. Origination and channel designation messages are discussed, for example, in TR45, TIA/EIA-136-123-A Draft Text, Digital Control Channel. Layer 3, Aug. 31, 1998, the disclosure of which is hereby incorporated herein in its entirety by reference.
Because the called party is another mobile terminal, the mobile switching center checks the HLR to determine the current location area (LA) for the called mobile terminal 37b if the called mobile terminal is active. A plurality of cells is assigned to a location area, and a mobile terminal updates its location with the cellular system only when the mobile terminal enters a new location area. Accordingly, location area updates are not needed every time a mobile terminal enters a new cell. While Digital Control Channel (DCCH) traffic may be reduced, pages for a called mobile terminal may need to be transmitted in all cells assigned to the location area.
The mobile switching center then issues a page message to all radio base stations supporting cells in the location area of the called mobile terminal 37b. Each of these radio base stations issues a page message on an appropriate paging subchannel. Because of the DCCH paging structure, however, a period of time as long as 1.28 seconds may pass before the page message can be issued. The page message wakes the called mobile terminal from its battery sleep mode, and the called mobile terminal 37b responds to the appropriate radio base station (now referred to as the called radio base station 32b) with a page response message to indicate the same.
The page response message is relayed from the called radio base station 32b to the mobile switching center, and the mobile switching center instructs the called radio base station 32b to assign a digital traffic channel to the called mobile terminal 37b. The mobile switching center then completes a communications path between the originating mobile terminal 37a and the called mobile terminal 37b using the two digital traffic channels.
The conventional cellular communications system of FIG. 1, however, may not support dispatch oriented group calls (also referred to as conference calls). Radio dispatch group communications systems are commonly used by emergency service providers such as police and/or fire departments to provide communications between a dispatcher and emergency personnel. For example, a police dispatcher can simultaneously call all on-duty police officers using a radio dispatch communications system. Alternately, a police office can quickly establish communications with other police officers and/or dispatchers simply by pressing a push-to-talk button on his radio. Similar radio dispatch communications systems may also be used by businesses such as trucking and/or taxi businesses.
In general, radio dispatch group communications systems provide one-to-many group communications as opposed to one-to-one communications provided by conventional cellular radiotelephone communications systems. Radio dispatch group communications are also preferably provided without the call setup delays that may be common in a conventional cellular radiotelephone communications system. For example, the time required to setup a call in a conventional IS-136 cellular radiotelephone system may be as long as 6 or 7 seconds including up to 1.28 seconds just to page the receiving cellular radiotelephone. This setup time, however, may be unacceptable for police and other radio dispatch group communications systems.
With the proliferation of cellular communications systems, there has been an effort to provide hybrid communications systems that can support both cellular radiotelephone communications as well as dispatch oriented group communications. Such a system has been developed, for example, by Motorola with service being offered by Nextel. A similar system has been developed by Ericsson (the assignee of the present application) under the name DAMPS-PRO. In particular, the DAMPS-PRO product provides cellular communications according to the IS-136 cellular communications standard, as well as dispatch oriented group communications for predefined user groups.
In the DAMPS-PRO system, intelligent group communications functionality is added to an IS-136 cellular communications system as shown in FIG. 3. This intelligent group communications functionality is provided by adding a group server 41, a group bridge 43, a local area network 45, and a group database 47. The cells, mobile switching center, home location register, public switched telephone network, and radio base stations provide cellular communications as discussed above with regard to FIGS. 1 and 2.
With regard to group calls, the group bridge provides a bank of telephony equipment which can initiate and receive radiotelephone calls, provide voice prompts, and respond to user inputs. The bridge also provides a group function that sums the audio from all parties within a designated group and distributes the summed audio to all parties. The server communicates with the mobile switching center via standard telephony signaling (such as defined by the SS7 standard) and controls the operation of the bridge equipment via the local area network.
The setup for a group call according to the DAMPS-PRO system is illustrated in FIG. 4. In general, a predetermined set of mobile terminals define a group which can communicate in the group call mode. Each of these mobile terminals may have standard cellular radiotelephone functionality whereby one-to-one communications can be provided after entering a telephone number and pressing a send button. Mobile terminals in a conference group may also include a push-to-talk (PTT) button which can automatically establish a group call with other active mobile terminals in the group.
In particular, an originating mobile terminal 37axe2x80x2 may issue an origination message when the PTT button is pushed. The radio base station providing service to the originating mobile terminal 37axe2x80x2 (now referred to as the originating radio base station 32axe2x80x2) receives the origination message, and checks the origination message for errors. If no significant errors are detected, the origination message is forwarded to the mobile switching center. The mobile switching center authenticates the originating mobile terminal 37axe2x80x2 and analyses the called number therein identifying the group. If the originating mobile terminal 37axe2x80x2 and the identified group are valid, the mobile switching center authorizes the originating radio base station 32axe2x80x2 to assign a digital traffic channel to the originating mobile terminal 37axe2x80x2, and a conversation channel is established between the originating mobile terminal 37axe2x80x2 and the group bridge 43 using the assigned digital traffic channel.
Group calls are indicated by a called party number portion of the origination message that is understood by both the mobile terminals in the group and the mobile switching center. The mobile switching center detects that the called party number is for a group call and connects the originating mobile terminal to the conference bridge. The conference server accepts the call and then searches the group database to determine the other mobile terminals in the group that should be called. The server then instructs the conference bridge to place calls to each of the other mobile terminals in the group via the mobile switching center. The call from the originating mobile terminal and the calls to each of the other mobile terminals in the group are then grouped together. In particular, the mobile switching center issues pages for each of the other mobile terminals in the group and completes each call normally once each serving radio base station is known. As further shown in the flow diagram of FIG. 5, the steps of sending the origination message at block 81, setting up the originating side of the call at block 83, paging to locate the called mobile terminals at block 85, and setting up the terminating side of the call at block 87 proceed sequentially.
As discussed above, however, an origination message according to the IS-136 standard may be transmitted over time slots in multiple time division multiple access (TDMA) time frames thereby increasing the time needed to set up a group call. The transmission of an origination message over multiple time frames may also reduce the probability that a complete origination message is correctly received by the communications system on the first transmission thereof. Accordingly, there continues to exist a need in the art for improved methods and systems for generating group call origination and other messages.
It is therefore an object of the present invention to provide improved methods and systems providing group call origination and other messages.
It is another object of the present invention to provide methods and systems that can reduce the time to set up a group call.
It is still another object of the present invention to provide methods and systems that can increase the probability that a group call origination message is correctly received at a radio base station.
These and other objects can be provided according to the present invention by receiving a login message at a radio base station from a mobile terminal wherein the login message includes a caller address number for the mobile terminal and wherein the caller address number comprises a first number of bits. After receiving the login message, a temporary identification number is selected at the radio base station for the mobile terminal wherein the temporary identification number comprises a second number of bits less than the first number of bits, and the temporary identification number is transmitted from the radio base station to the mobile terminal. After transmitting the temporary identification number, a digital information message is received at the radio base station from the mobile terminal wherein the digital information message includes the temporary identification number and payload information. By assigning a relatively short temporary identification number to the mobile terminal, subsequent messages from the mobile terminal to the radio base station can include more payload information.
In addition, the caller address number can be saved at the radio base station. Accordingly, the temporary identification number in the digital information message can be used to determine at the radio base station the caller address number for the mobile terminal. The radio base station can thus send the caller address number and the payload information to the switching center. Accordingly, the use of the temporary identification number can be made transparent to the switching center so that radio base stations according to the present invention can be used with conventional switching centers produced by other manufacturers.
By using the relatively short temporary identification number, messages such as group call origination messages can be sent and received over a single time slot of a time division multiple access (TDMA) radio channel of a communications standard such as the IS-136 communications standard. The time to send these messages can thus be reduced, and the probability of receiving these messages without corruption can be increased. More particularly, the digital information message can include a caller address field and a payload field, wherein the temporary identification number is received in a first portion of the caller address field, and wherein a first portion of the payload information is received in the payload field and a second portion of the payload information is received in a second portion of the caller address field. According to the IS-136 communications.standard, for example, the caller address field of a conventional message includes a 34 bit mobile identification number. According to the present invention, the use of a shorter temporary identification number allows additional payload information to be sent in a portion of the caller address field of the message.
In particular, the digital information message can be an origination message for a group call and the payload information can include a group number identifying a group of mobile terminals to be included in the group call. Because the origination message for the group call can be transmitted as a single slot message over a single slot of a single TDMA time frame of a digital control channel (DCCH), the group call can be established more quickly and more reliably. This is particularly useful for group dispatch communications used by emergency service providers such as police and fire departments where rapid call setup is important. In these types of applications, group dispatch communications may include many short calls with each call requiring the transmission of a group call origination message over a digital control channel. By providing each group call origination message over a single time slot of a single DCCH time frame, loading of the DCCH capacity can also be reduced.
The present invention can also include receiving a second login message from the mobile terminal at a second radio base station of the communications system wherein the second login message includes the caller address number for the mobile terminal. After receiving the second login message, a second temporary identification number is selected at the second radio base station for the mobile terminal wherein the second temporary identification number comprises a third number of bits less than the first number of bits. The second temporary identification number is transmitted from the radio base station to the mobile terminal. After transmitting the second temporary identification number, a second digital information message is received at the second radio base station from the mobile terminal wherein the second digital information message includes the second temporary identification number.
According to the present invention, more payload information can be included in a single slot message transmitted over a single time slot of a single time division multiple access time frame. A group call origination message transmitted as a single slot message according to the present invention can thus speed the setup of a group call.